A user equipment (UE) may be configured to establish a connection to at least one of a plurality of different networks or types of networks to perform a variety of different functionalities via the network connection. For example, the UE may communicate with another UE through the network connection. Specifically, the communication may be a Voice over Internet Protocol (IP) (VoIP) call. Accordingly, the UE may register with an IP Multimedia Subsystem (IMS) for the VoIP functionality to be performed.
The VoIP call may be performed over different types of networks. For example, when performed over a Long Term Evolution (LTE) network, the VoIP call is referred to as a VoLTE call. In another example, the VoIP call may be performed over a WiFi network that is configured to utilize IP. Thus, when utilizing the LTE network, the UE may register with the IMS core network over an IMS bearer to be established over LTE. Similarly, when utilizing the WiFi network, the UE may register with the IMS core network over an IPSec tunnel to an IMS core established over WiFi. When the IMS bearer is established, the UE and the network associate this IMS bearer with a packet data protocol (PDP) context in case of both LTE and WiFi. Specifically, when the IMS bearer over the LTE network or over WiFi is established and information corresponding thereto is provided to the UE, the UE may store a context associated therewith relating to a respective network state of the UE. Thus, when utilizing services via IMS, the PDP context provides a pipe to the core IMS core network for IMS session initiation protocol (SIP) signalling. This PDP context is created at UE boot up and remains activated until deactivated. While a PDP context is up and activated, the UE will not attempt to bring up the PDP context again.
The UE may be a mobile device capable of moving from one location to another. This may enable the UE to roam from a first network using a first connection to a second network using a second connection. For example, the UE may roam from a LTE network to a WiFi network. With respect to the IMS bearer, the networks may perform a variety of different operations such as establishing the IMS bearer over the network to which the UE has roamed (e.g., the WiFi network) while releasing the IMS bearer over the network from which the UE has roamed (e.g., the LTE network).
When the UE is in a radio resource control (RRC) connected state, the UE may be provided information about the IMS bearers such that the UE is synchronized with all associated networks by updating the respective network states of the UE in each of these associated networks. For example, the UE may receive information that the WiFi network has established the IMS bearer over the WiFi network for the UE and store a corresponding context while the LTE network has released the IMS bearer for the UE such that the UE may delete the context for the IMS bearer over the LTE network. However, when the UE is in a RRC idle state, and the UE has roamed from the LTE network to the WiFi network while in the RRC idle state, and the UE has subsequently established the IMS bearer over the WiFi network, the UE only receives information about the IMS bearer over the WiFi network being established. That is, the UE still has the context for the IMS bearer over the LTE network despite the LTE network having released the IMS bearer for the UE due to the roam. Therefore, the UE only updates the WiFi network state of the UE but not the LTE network state. Accordingly, the UE is not synchronized with all associated networks regarding bearer information. This may cause a variety of issues, especially when the UE roams back to the LTE network while in a RRC idle state relative to the LTE network. For example, a VoIP call may be dropped since the UE performs operations based upon out-of-date information that the IMS bearer over the LTE network is still valid.